Control of iron deposition in borehole pumps

ABSTRACT

Method and apparatus for the control of deposition of contaminants in pumping systems. The method includes the steps of periodically stopping the pump and back feeding chlorinated water and/or surfactants and other organic or inorganic acids at a reduced flow rate through the outlet pipe of the pump and through the pump itself to control the deposition of materials by bacterial action and/or to control biofouling and/or abiotic encrustation. The apparatus includes a bypass and valving to provide a back flow of the chlorinated water and/or surfactants and other organic or inorganic acids through the pumping installation at a relatively slow flow rate and equipment for the feeding desired decontaminants into the back flow.

This invention relates to methods and apparatus for the control ofmicrobial encrustation (biofouling) and microbial corrosion in groundwater pumping systems.

BACKGROUND OF THE INVENTION

The major processes that cause deterioration of ground water bores(wells) are physical, chemical, and microbial. The resultant problemsaffect parts of the pumping system; bore, aquifer, pump, discharge anddistribution components. In some cases some of the processes cansimultaneously affect parts of the system to differing degrees.

Ground water typically contains a wide range of dissolved chemicals butin the absence of external contamination, aquifers were once assumed tobe microbiologically clean. However, it is now recognised that bacteriaare endemic in aquifers throughout the world and that aquifers can allowthe free transmission of bacteria under suitable conditions. Given asuitable physical and chemical environment, bacteria can thrive and giverise to a multitude of problems.

The phenomenon of microbiological encrustation (biofouling) is now wellrecognised world wide. It is caused by the accumulation of microbes(bacteria, often called "iron related bacteria"), extracellularpolymeric substances and inorganic precipitates, typically iron,manganese, aluminium or other oxides. In the case of iron, the bacteriaderive energy during their metabolism through oxidising soluble ferrousiron to insoluble ferric iron. The resultant biofilm is commonly foundas a slimy or gelatinous deposit in bore screens, pump inlets, internalwaterways and discharge components, sometimes extending well into thedistribution pipe system.

Depending on the severity of the biofouling, various detrimental effectsmay occur including:

Degraded water quality (colour, taste, odour)

Reduced hydraulic efficiency due to clogging of the gravel-pack screenslots, pump and pipework

Corrosion of materials due to the creation of adverse electrochemicalconditions

Other types of bacteria cause corrosion problems such as:

Sulphate oxidising bacteria produce sulphuric acid

Sulphate reducing bacteria produce a variety of substances includinghydrogen sulphide

Fermentation process produce organic acids

Many techniques have been used to rehabilitate bores:

Physical methods include high pressure water jetting, compressed airsurging and brushing or swabbing.

Chemical methods, often used in conjunction with physical agitationinclude the use of organic or inorganic acids in conjunction withsurfactants and biocides such as chlorine, hydrogen peroxide andquaternary ammonium compounds. Many proprietary bore cleaning productsare available using various combinations of these chemicals.

Such treatments often have to be repeated regularly and can be timeconsuming to carry out, result in significant loss of pumping time, canbe very expensive if large quantities of chemical are required andsometimes require considerable ancillary mechanical equipment such aspumps, compressors, and cranes etc.

It would be preferable to implement a system to prevent or control thebuild up of bacteria in a ground water pumping system by regulardisinfection rather than undertaking remedial treatment once the problemhas become intolerable.

The problem of dissolved iron in ground water has attempted to beovercome by Patent No SU 1504226 which involves a vacuum section toremove gasses in the water followed by an aeration section with a filterto remove trivalent iron. Also Patent No CN 87106661 uses oxygenaeration to remove iron and manganese from ground water. SU 1161480describes the use of atmospheric air to remove dissolved iron, while DE3333842 describes removing iron and manganese from water wells byadmitting compressed air to one or two wells in turn. AU8429683describes a method where oxygen containing water is injected into theground water and removing cleansed water from the ground water around oradjacent the point of injection. SU 859322 describes passing the waterthrough a filter or bed which is provided with a negative potential toremove the iron.

It is an object of this invention to provide a solution to the aboveproblems and to provide control measures which should minimise theforegoing factors.

While chlorine is known to be effective in controlling bacteria theinvention has an object to provide a simple and economical process forthe in situ electric generation of chlorine from the ground water beingpumped if it has a high enough chlorine content.

The principle of electrolytic generation of chlorine from salt water orconcentrated brine (sodium chloride) solutions is widely used inindustry and in domestic salt water swimming pools. However ifelectrolytic generation is used to generate a sufficiently highconcentration of chlorine to be effective in the high flow rates oftenrequired for pumping ground water, the costs could be excessive. Thus ifa pump flow of 4.0L/s is required, an appropriate size electrodeassembly running at greater than 50 Amps may be necessary to maintain achlorine residual of 1.0ppm depending on the chemical composition of thewater being pumped.

In many situations it may not be physically or economically feasible toinstall an electrode assembly of sufficient chlorine production capacitydown a bore at the inlet to the pump.

It has been found that with the installation of a surface mountedchlorinator which has many advantages over a down the hole installationand periodically back flushing the pump and lines with chlorinated waterthat effective control of biofouling or abiotic encrustation(non-bacterial accumulation of material) can be achieved.

In situations where the groundwater does not have a high enough chloridecontent to permit the production of electrolytically generated chlorine,the back flushing of the pump and lines with a disinfectant or biocidehas been found to be equally effective.

BRIEF STATEMENT OF THE INVENTION

Thus there is provided according to the invention a method ofcontrolling deposition of biofouling or abiotic encrustation ingroundwater pumping installations, the method including the steps ofperiodically stopping the pump and backfeeding chlorinated water and/orsurfactants and other organic or inorganic acids at a reduced flow ratethrough the outlet pipe and thus through the pump itself to control thedeposition of materials by bacterial action and to control biofoulingand/or abiotic encrustation.

In a further form of the invention the method includes the controllingof the deposition of materials such as iron through bacterial action insaid pumping installation by a submersible pump connected by a riser toa reflux valve, by the steps of periodically stopping the pump andbackfeeding electrolytically generated chlorinated water at a muchreduced flow rate via bypass passage around the reflux valve and downthe riser through the pump itself.

Also there is provided according to the invention apparatus to controlthe deposition of biofouling or abiotic encrustation in a groundwaterpumping installation, said apparatus including control means to providea back flow of water through the pumping installation at a reduced flowrate, and feeding means to feed decontaminants into said back flow, saiddecontaminants being selected from chlorinated water, disinfectants orbiocides such as hydrogen peroxide and quaternary ammonium compounds andorganic or inorganic acids.

In a preferred form of the invention there are provided means to by-passa reflux valve so that water at a reduced rate can be passed down theriser and through the pump itself, the backflow water passing through achlorinator and bypassing the reflux valve to thus control the bacterialaction causing the deposition of iron in the pump and riser.

While the following description is directed primarily to the passage ofwater through a chlorinator,it is to be realised that the invention isnot to be limited thereto but aqueous chlorine or other liquid orgaseous substances can be introduced from a container via a contolvalve, venturi injector or metering pump with the overall objective ofcontrolling bacterial build up in the pump or well or inducing chemicalprecipitation or removing organic or inorganic deposits.

Thus by this method, using a much reduced flow of water, the desiredchemical concentration can be achieved and the down time of the pumpwhen the pump is stopped for the reverse flushing of the riser and pumpneed only be up to an hour a day.

While aqueous chlorine is commonly available, any other form of liquidor gaseous disinfectants or biocides such as hydrogen peroxide andquaternary ammonium compounds can be used with equal effectiveness, ifnecessary in conjunction with surfactants and other organic or inorganicacids to control biofouling and abiotic encrustation (non-bacterialaccumulation of material) within the bores.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more fully describe the invention reference will now be madeto the accompanying drawings in which:

FIG. 1 schematically shows one form of the invention for use withsubmersible pumps,

FIG. 2 shows another form of the invention for use with surface mountedpumps,

FIG. 3(a) shows a metering pump,

FIG. 3(b) shows a venturi type injector, and

FIG. 3(c) shows hydraulically or pneumatically solenoid operated valves.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring firstly to FIG. 1 which shows the invention as applied tosubmersible pumps which are often commonly employed in pumping groundwater, the upper portion of the riser 1 is connected to the riser column2 which is in turn connected to a pump (not shown) at the bottom of theriser column. The riser 1 is connected to a reflux valve 3 which in turnis connected to the chlorinator assembly 4 positioned in line 5 upstreamof the discharge line 6. Between line 5 and the riser 1 there isconnected a bypass line 7 with control valves 8 (a), (b) and (c) andcontrol valve 9. The chlorinator is connected via electrical leads 10 toa DC power supply.

Thus when it is desired to periodically reverse flush the pump and riserwith chlorinated water, the pump is stopped and the reflux valve closes.Valves 8(a) and 8(b) are normally open and the chlorinator assembly isthen energised with electrical power. Water is then caused to flow at aslow rate through the chlorinator assembly where the water is chargedwith chlorine at the desired high rate, this passing via the bypass linearound the reflux valve down the riser and through the submerged pumpand into the bore and adjacent aquifer. The water flow during pumping isshown in solid line arrows, while the reverse flow is shown broken linearrows. Valve 9 is the main control valve for the bypass system. Valve8(c) is normally closed, and is opened when it is desired to test thedegree of chlorination of the reverse flow water.

Depending on the pumping installation, as noted above the back flow ofwater is relatively slow. This is necessary for the chlorinated water tobe effective in controlling the bacterial growth, and it has been foundthat a flow rate of between 2 to 10 liters per minute is quiteeffective. Also the dosage of chlorine has to be sufficient to beeffective and a dosage rate of between 1 to 4 parts per million resultsin effective reduction in the bacterial growth.

Tests have shown that when the invention was applied to existing pumpswhich had their flow rates reduced due to an accumulation of iron, theflow rates increased after treatment due to the removal of a proportionof the accumulated iron. When the invention is fitted to new orreconditioned pumps, the flow rates are not reduced. However ininstances where the chlorinator was accidentally turned off, the flowrate reduced rapidly due to the accumulation of iron.

While the invention has been particularly directed to the control ofbacteria in the underground water deposition of iron, the invention isnot to be limited thereto, but is intended to control the deposition ofmanganese or other cations which may react with chlorine or otherintroduced chemicals or the growth of bacteria.

Turning now to FIG. 2, this shows an installation where the pump 11 ismounted on the surface, the riser 2 being the suction pipe of the pump.The bypass 7 again by passes the reflux valve and is connected to theoutlet 12 of the pump 11. The chlorinated reverse flow water thus againpasses through the pump and down the riser to the aquifer below.

In circumstances where it is not possible to develop chlorine from thewater being pumped, chlorine or other substances can be introduced intothe pump and bore by various methods. Thus FIG. 3(a) shows a reservoir14 for the chemical substance to be dosed into the return flow of water.This dosing is controlled by a metering pump 15 which delivers thecontrolled amount of substance as demanded by the control system. Thesubstance is delivered into the outlet of the pump to thus pass throughthe pump into the aquifer. In this instance the pumping installation maybe such that it is not possible to produce a backflow of water throughthe pump due to a lack of head of water in the discharge pipe. Thusthere is provided the reservoir 14 which is sufficient in capacity toprovide the required backflow through the pump. The water in thereservoir may have the desired chemical substance added thereto asdesired.

FIG. 3(b) shows a further example where the chemical substance in areservoir or container 16 is passed through a control valve 18 to aninjector 17 positioned in the bypass line 19.

A further example is shown in FIG. (3C) where there is provided areservoir 14 of water and the chemical substance, the water being fedthrough a control valve 18 and solenoid or hydraulically orpneumatically operated valve 20 into the outlet of the pump. This flowof water and substance is sufficient to create the required back flowthrough the pump and riser.

While the examples given in FIG. 3 are illustrative of a surface mountedpump, it is to be realised that these chemical dosing arrangements canalso be implemented for submersible pumps.

Thus it can be seen that according to the invention there is provided asimple and effective method and apparatus to overcome the objects of theinvention. By utilising the back flow principle, say for one hour perday, the build up of contaminants in the pumping system is virtuallyprevented, and there is a minimum of downtime for the pump.

Although various forms of the invention have been described in somedetail, it is to be realised that the invention is not to be limitedthereto, but can include variations and modifications falling within thespirit and scope of the invention.

I claim:
 1. A method of controlling deposition of biofouling or abioticencrustation in a groundwater pumping installation having a submersiblepump connected by a riser through a reflux valve to an outlet pipethrough which ground water is pumped at a first flow rate, which methodcomprises the steps of periodically stopping the pump and backfeedingchlorinated water or surfactants or other organic or inorganic acids viaa by-pass passage around the reflux valve and down the riser and throughthe pump itself at a second flow rate reduced relative to the first flowrate to control the deposition in the pumping installation of materialsby bacterial action, or to control biofouling or abiotic encrustationtherein.
 2. The method as defined in claim 1, wherein the step ofbackfeeding comprises backfeeding electrolytically generated chlorinatedwater through the pumping installation.
 3. Apparatus for controlling thedeposition of biofouling or abiotic encrustation in a groundwaterpumping installation, wherein the pumping installation comprises asubmersible pump connected to a riser and an outlet pipe through whichgroundwater is pumped through the installation at a first flow rate, areflux valve in the outlet pipe, bypass means in the outlet pipe forbypassing the reflux valve, control means for providing a back flow ofwater through said bypass means and through said pumping installation ata second flow rate reduced relative to the first flow rate, and feedingmeans for feeding decontaminants into said back flow, saiddecontaminants being selected from the group consisting of chlorinatedwater, disinfectants, and biocides.
 4. Apparatus as defined in claim 3,wherein said riser has a bottom portion connected to said pump and anupper portion connected to said outlet pipe, and an electrolyticchlorinator connected to said outlet pipe, so that the backflow of watercan bypass the reflux value and pass through the chlorinator to controlthe deposition of iron in the pump and riser.
 5. Apparatus as defined inclaim 4 wherein the bypass means is a passage connected to the outletline downstream of the reflux valve and upstream of the reflux valve,and control valves are positioned in the said passage, and wherein thefeeding means comprises a venturi positioned in said passage andconnected to a source of decontaminating liquids selected from the groupconsisting of hydrogen peroxide, quaternary ammonium compounds, andsurfactants and acids to control biofouling or abiotic encrustation. 6.Apparatus as defined in claim 3 wherein the pumping installation furthercomprises a riser having a lower portion connected to said pump, asurface pump connected to an upper portion of the riser, the riserforming the suction line of the surface pump, and by-pass means forpassing the backflow water through the surface pump and down the riser.7. Apparatus as defined in claim 3 wherein the pump is a submersiblepump, and the bottom portion of the riser is connected to the outlet ofthe pump, so that the backflow water passes down the riser and thenthrough the pump.
 8. Apparatus as defined in claim 3 wherein the feedingmeans is a metering pump.
 9. Apparatus as defined in claim 3 wherein thefeeding means comprises a reservoir of water and decontaminatingsubstances, and valve means to regulate the flow of water into thepumping system sufficient to create the backflow of water.
 10. Theapparatus defined in claim 3, wherein the biocides are selected from thegroup consisting of hydrogen peroxide, quartenary ammonium compounds,and organic and acids and inorganic acids.